English: 3D model representation of a radio alternator, a specialized high speed alternating current electric generator invented by Nikola Tesla in 1891 to generate high frequency current. It was an induction generator with 384 magnetic poles. When rotated at 3000 RPM it could generate 10 kilowatts at a frequency of 10 kilohertz (10,000 cycles per second). Tesla demonstrated it in his lecture before the American Institute of Electrical Engineers at Columbia College, May 20, 1891.

After radio waves were discovered by Hertz in 1887, the first generation of radio transmitter, the spark gap transmitters, produced strings of damped waves, pulses of radio waves which died out to zero quickly. By the 1890s it was realized that damped waves had disadvantages and efforts were made to invent transmitters that would produce continuous waves, a sinusoidal alternating current at a single frequency.

In an 1891 lecture, Frederick Thomas Trouton pointed out that, if an electrical alternator had enough poles on its armature and were run at a high enough speed, it would generate continuous radio frequency waves. Starting with Elihu Thomson in 1889, a series of researchers built high frequency alternators, Nikola Tesla (above), Salomons and Pyke (1891, 9 kHz), Parsons and Ewing (1892, 14 kHz.), Siemens (5 kHz), B. G. Lamme (1902, 10 kHz), but none were able to reach radio frequencies. In 1906, Reginald Fessenden invented the first alternator that could generate radio waves, producing frequencies up to 100 kHz. This became the first alternator radio transmitter, the Alexanderson alternator. (Info from John Ambrose Fleming (1910) The Principles of Electric Wave Telegraphy and Telephony, Longmans, Green and Co., London, p. 5-13)

You can download this 3D model at:

http://www.blendswap.com/blends/electronics/tesla-the-high-frequency-alternator/